Method and communication system for estimating an error covariance matrix for the downlink in cellular mobile radio telephone networks with adaptive antennas

ABSTRACT

Data is transmitted in a radio communication system having two or more base stations that are located in the network and having additional radio stations, which are each connected to one of the base stations via radio interfaces. At least one first base station has an antenna array with a multitude of antenna elements and with a signal processing device for the directional transmitting-receiving of data. The first base station temporally overlays data to a radio station, which is connected to the base station, for the transmission of data from an external base station to an external radio station connected thereto. The transmission of data from the first base station is also received from the external radio station. The objective is to reduce the amount of disturbance to the external radio station caused by transmissions from the base station in the downlink direction. To this end, the transmitting power of the antenna array of the base station is reduced in the direction toward the external radio station after a transmission of a training signal of the transmitted signal for the external radio station and after the reception of an assignable training signal of the external radio station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to GermanApplication No. 100 252 87.7 filed on May 22, 2000, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to directionally dependent control of the powerfor the downlink in a cellular radio communication network with adaptiveantennas.

In radio communication systems, information (for example speech, imageinformation or other data) is transmitted with the aid ofelectromagnetic waves via an air interface between transmitting andreceiving stations (base station and subscriber station, respectively).The emission of the electromagnetic waves is performed in this case withthe aid of carrier frequencies that are in the frequency band providedon the respective system. In the case of the GSM (Global System forMobile Communication), the carrier frequencies are at 900, 1800 and 1900MHz. Frequencies in the frequency band of approximately 2000 MHz areprovided for future mobile radio systems using CDMA or TD/CDMAtransmission methods via the radio interface, for example the UMTS(Universal Mobile Telecommunication System) or other 3rd generationsystems.

The data transmission takes place via frames in the case of these radiocommunication systems. A division of a broadband frequency domain into aplurality of time slots of equal time duration is provided in the caseof a TDMA component (TDMA: Time Division Multiple Access). The timeslots are used partially in the downlink DL (downlink from base stationto subscriber station), and partially in the uplink UL (uplink fromsubscriber station to base station). One or more switching points aresituated therebetween. The same is repeated for further carrierfrequencies. Information of a plurality of connections is transmitted inradio blocks within the time slots. Radio blocks for user datatransmission currently include sections with data in which trainingsequences or midambles known at the receiving end are embedded.

The switching points can be defined synchronously in all cells of theradio communication system. In this case, a time slot in the overallradio communication system is used exclusively in the uplink UL orexclusively in the downlink DL. Additional flexibility is achieved bydefining the switching points asynchronously. In this case, some cellsof the radio communication system use one time slot for UL and othersfor DL.

Because the distance between transmitter and receiver frequentlyfluctuates strongly during operation, it is desired to match thetransmit power over up to a plurality of orders of magnitude, in orderto keep the ratio of energy per bit/noise-power density or the ratio ofsignal/interferer or carrier power/ interference power in the limit ortarget range. On the one hand, the receive power must be at a minimumlevel that is required for the desired surface quality, but on the otherhand as little interference as possible is to be produced.

DE 198 03 188 discloses a method and a base station for, in particular,TDMA/CDMA transmission methods (CDMA: Code Division Multiple Access), inthe case of which the signals transmitted from the base station in thedownlink are specifically amplified in the direction of the assignedsubscriber station, and attenuated in the other directions. For thispurpose, spatial covariance matrices are estimated in the base stationfor each subscriber station in order to determine amplifyinginterference from the signal received in the uplink, and thereafter abeam-shaping vector is calculated which maximizes the signal/noise ratioat the receiver. A general eigenvalue problem is solved in this casewithout iteration. Thereupon, transmitted signals are weighted with thebeam shaping vector for the corresponding radio link and fed to theantenna element of the antenna arrangement for emission. The covariancematrix is determined from a priori assumptions with the aid of amathematical model. The base station measures nothing during thetransmission to its subscriber station in the corresponding downlinktime slot. Consequently, uplink measurements of the training sequencesmust be used for estimation, in order to estimate the downlinkcovariance matrix.

In other words, in the case of this method the antenna gain of theantenna arrangement of the base station is maximized in specificdirections, which are assigned to the dedicated subscriber stations, byappropriately driving the individual antenna elements of the antennaarrangement. That is to say, the power that is transmitted from anantenna group to an assigned subscriber station is emitted in amaximized fashion by constructive interference in the direction in whichthis subscriber station is located.

These radio communication systems have a cellular structure in which ineach case a base station with at least one transmitting antennaarrangement supplies subscriber stations in a specific radio cell zone.In this case, disturbing interference with subscriber stations ofadjacent radio cell zones can arise that are supplied from a neighboringbase station. This is the case, in particular, when the base stationtransmits to a subscriber station assigned to it in a time slot in whichthe subscriber station in the adjacent radio cell zone receives datafrom its base station, the adjacent one.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method for reducing thedownlink transmit power which disturbs subscriber stations in adjacentcells, and a cellular radio communication network with adaptive antennasfor carrying out such a method.

In the case of a method according to the present invention, theinterference at foreign subscribers is advantageously minimized bymaximizing the transmit power for dedicated subscribers of atransmitting or base station. In this case, the radio waves are directedin the direction of the desired dedicated subscriber stations and, inaddition, the transmit power in other directions is minimized.

The use of the method or of the radio communication system is suitable,in particular, for mobile radio networks that use a time division duplex(TDD) method with adaptive antenna groups. In the case of the plannedsystems, these are, for example, UMTS UTRA-TDD and TD-SCDMA for China.

The use in FDD systems, for example GSM, is possible by means of afrequency transformation that is carried out before the estimated uplinkcovariance matrices can be used for application as downlinks.

In the case of asynchronous switching points, it is advantageous also totake account of the training signals of those foreign network-side basestations that transmit downlink in an uplink time slot of the basestation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a block diagram of a mobile radio system,

FIG. 2 is the frame structure of a known TDD transmission method, and

FIG. 3 is a simplified block diagram of a base station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

The mobile radio system illustrated in FIG. 1 as an example of a radiocommunication system includes a multiplicity of mobile switching centersMSC that are networked to one another and/or provide access to a fixednetwork PSTN or packet data network GPRS. Furthermore, these mobileswitching centers MSC are connected to in each case at least one deviceRNM for allocating radio resources. Each of these devices RNM in turnrenders it possible to make a connection to at least one base stationBS, here the base stations BS and an adjacent base station BSn. Such abase station BS can set up via an air interface V a connection tosubscriber stations, for example mobile stations MS or other types ofmobile and stationary terminals. At least one radio cell Z is formed byeach base station BS. A plurality of radio cells Z can also be suppliedper base station BS in the case of sectorization or of hierarchic cellstructures.

Existing connections V1, V2 for transmitting user information andsignaling information between subscriber stations MS and a base stationBS, as well as a request for resource allocation or a shortacknowledgement message in an access channel RACH by a furthersubscriber station MS are illustrated in FIG. 1 by way of example. Theadjacent base station BSn is connected to a further subscriber stationthat is also denoted below from the point of view of the base station BSforeign to it as foreign or adjacent subscriber station MSn.

Also illustrated is an organization channel (BCCH: Broadcast ControlCHannel) that is provided for transmitting user and signalinginformation with a defined transmit power from each of the base stationsBS for all subscriber stations MS.

An operation and maintenance center OMC implements monitoring andmaintenance functions for the mobile radio system or for parts thereof.The functionality of this structure can be transferred to other radiocommunication systems, in particular for subscriber access networks withwireless subscriber access.

The frame structure of the radio transmission may be seen from FIG. 2.In accordance with a TDMA component (TDMA: Time Division MultipleAccess), a division of a broadband frequency band, for example thebandwidth B=5 MHz, is divided into a plurality of time slots ts of equaltime duration, for example 16 time slots ts0 to ts15. A frequency bandextends over a frequency domain B. A portion of the time slots ts0 tots8 is used in the overall radio communication system in the downlinkDL, and a portion of the time slots ts9 to ts15 is used in the uplinkUL. Situated therebetween are one or more synchronous switching pointsSP—only one switching point in FIG. 2. In the case of this TDDtransmission method, the frequency band for the uplink UL corresponds tothe frequency band for the downlink DL. The same is repeated for furthercarrier frequencies.

Information of a plurality of connections is transmitted in radio blockswithin the time slots ts. Function blocks for user data transmissioninclude sections with data d in which training sequences or midamblesma1 to ma-n known at the receiving end are embedded. The data d with 1 .. . N symbols are spread individually by connection with a finestructure, a subscriber code c, such that, for example, n connectionscan be separated at the receiving end by means of these CDMA components(CDMA: Code Division Multiple Access). A physical channel is formed inthis case by a frequency band B, a time slot, for example ts6, and asubscriber code c. A plurality of physical resources are generallylinked to a logic channel in order to transmit services at high datarates. For example, 8 physical resources are required in each case forthe service 144 kbit/s in uplink and downlink.

The spreading of individual symbols of the data d has the effect that Qchips of duration Tchip are transmitted within the symbol duration Tsym.The Q chips in this case form the connection-specific subscriber code c.Furthermore, a guard period gp for compensating different travel timesof the signals of the connections is provided within the time slot ts.

As may be seen from FIG. 3, the base station BS has atransmitting/receiving device TX/RX that subjects the transmittedsignals to be emitted to digital/analog conversion, transforms them fromthe baseband into the frequency domain B of the emission, and modulatesand amplifies the transmitted signals. The amplified signals are thenfed to the intelligent and/or adaptive antenna arrangement with theantenna elements A1-A4. A signal generating device SA has previouslyassembled the transmitted signals in radio blocks and assigned them tothe corresponding frequency channel TCH. A signal processing device DSPevaluates received signals received via the antenna arrangement and thetransmitting/receiving device TS/RX, and executes a channel estimation.

In order to reduce the interference of the base station BS, also denotedbelow as interfering base station BS, exerted on the adjacent anddisturbed subscriber station MSn, an error covariance matrix isestimated in the disturbing base station BS. While the known covariancematrices serve the purpose of amplifying the transmitted signals in thedirection of the communicating subscriber stations MS, the errorcovariance matrix is formed in order to reduce the transmit power in thedirection of the adjacent, disturbed subscriber station(s) MSn.

Correlation signals are transferred to the disturbing base station BSfrom the adjacent base station BSn, which is connected to orcommunicates with the subscriber station MSn assigned to it anddisturbed. In the case illustrated, the correlation signals aretransferred via the lines L1 and L2, which connect the two base stationsBS, BSn to the device RNM for administering radio resources.

Here, the disturbed subscriber station MSn transmits the trainingsequence(s) ma-n and/or the code of the training sequence(s) ma-n ascorrelation signals. The disturbing base station BS thereby detects thesignal of the foreign, disturbed subscriber station MSn, and cansimultaneously determine the intensity of this signal. Moreover, thedisturbing base station BS can use its antenna arrangement with theantenna elements A1-A4 to determine or estimate the direction from whichthis signal arrives, and thus the direction in which the disturbedsubscriber station MSn is located.

Using the received training sequence(s) ma-n, which are currently formedby a coded pilot signal, the disturbing base station BSn thencorrespondingly carries out a channel estimate for one or more foreignsubscriber stations MSn.

The result in the final analysis is the formation of an error covariancematrix R_(I) ^((k)) that is used to minimize the disturbing transmittedsignal to the disturbed subscriber station MSn. The determination of theerror covariance matrix R_(I) ^((k)) for the purpose of reducing orminimizing the transmit power in the direction of foreign, disturbedsubscriber stations MSn is performed in this case in a way comparable tothe determination, known per se from DE 198 03 188 A1, of the covariancematrix R_(S) ^((k)) for maximizing the transmit power in the directionof dedicated subscriber stations MS. The same holds for thedetermination of corresponding beam-shaping vectors w^((k)), generalizedeigenvalues λ^((k)) and the estimated uplink channel pulse responsematrices H^((k)).

Finally, the ratio

${r\left( w^{(k)} \right)} = \frac{w^{{(k)}H}R_{S}^{(k)}w^{(k)}}{w^{{(k)}H}R_{I}^{(k)}w^{(k)}}$is maximized, the index k with 1≦k≦K and K as the number of thesubscriber stations MS to be taken into account. In this case, the beamshaping vectors w^((k)) are an M-dimensional vector with M (with M=4 inFIG. 3) as the number of the antenna elements A1-A4 of the antennaarrangement of the disturbing base station BS.

The quadratic Hermitian and positive-definite error covariance matrixR_(I) ^((k)), the number of whose rows and columns corresponds to thenumber M of the antenna elements A1-A4, is formed from the sum of thetotal of L error covariance matrices R_(ad) ^((I)) for the individualdisturbed subscriber stations MSn of the adjacent radio cells Zn. Itholds that:

$R_{I} = {{\sum\limits_{l = 1}^{L}{R_{ad}^{(1)}\mspace{14mu}{with}\mspace{14mu} R_{ad}^{(1)}}} = {{\frac{1}{W} \cdot H^{(l)}}H^{{(1)}H}}}$H^((I)) corresponding to the estimated uplink channel pulse responsematrix of the I-th disturbed subscriber station MSn, and the superscriptH marking the transjugation (“Hermitian operation”). In order to improvethe accuracy of estimation, the estimates of the spatial errorcovariance matrix R_(I) ^((I)) can be undertaken by using a rectangularor exponential window over a plurality of time slots that may stem fromdifferent frames. The subscriber-specific contribution can be identifiedby correlation with the sets, transferred via the communication network,of training sequences ma-n. Consequently, the disturbing base station BScan synthesize a predicted interference error covariance matrix R_(I)^((I)) for the downlink DL for the subscriber stations MSn that areactive in a downlink time slot DL-ts.

Each base station BSn can automatically transmit all the trainingsequences ma-n, which are newly allocated in their radio cell zone Z, tothe adjacent base stations BS. Alternatively, however, it is alsopossible to reduce the signaling outlay by specifically transmittingtraining sequences ma-n when a subscriber station MSn establishes thatit is receiving signals from a foreign base station.

The transmission of training sequences ma-n is preferably performed withthe aid of a protocol that is, in particular, set up appropriately onthe side of the network (RAN/Radio Access Network) of the radiocommunication system.

The protocol informs the adjacent, disturbing base stations BS at leastas to which subscriber stations MSn have been allocated which uplinktraining sequences ma-n. If the disturbing base station BS receives sucha training sequence ma-n, which permits a unique identification, the(disturbing) base station BS can therefore assign this received signalto the (disturbed) foreign subscriber station MSn. The (disturbing) basestation BS is therefore capable of initiating an estimate of eachcontribution to the error covariance matrix which stems from the foreignsubscriber station MSn.

In the case of a particularly preferred embodiment, the protocol informsthe disturbing base stations BS as to which subscriber stations MSn havebeen allocated which uplink training sequences ma-n in which uplink timeslots UL-ts. In this embodiment, it is assumed that a fixed assignmentbetween uplink time slots UL-ts and downlink time slots DL-ts exists inthe radio communication system. This is a preferred embodiment forsymmetric services that exhibit equally large traffic loading in bothdirections of connection, as is the case, for example, in transmittingspeech.

If such a fixed assignment cannot be assumed between UL-ts and DL-ts,the protocol of the above-named advantageous embodiment is extended. TheBS is now additionally informed as to in which downlink time slots DL-tsthe subscriber stations MSn are to receive signals or data from theirbase station BSn.

The base stations BS, BSn thus administer an association table MEMsketched in FIG. 3, that contains data relating to adjacent subscriberstations MSn, their training sequences ma-n and, preferably, thedownlink time slots DL-ts assigned to the latter. Of course, it followstherefrom that the disturbing base station BS receives and administersin the uplink not only the signals of the dedicated subscriber stationsMS, but also the signals of the foreign disturbed subscriber stationsMSn. In the downlink, by contrast, the signals to the dedicatedsubscriber stations MS are amplified, and the signals in the directionof the foreign disturbed subscriber stations MSn are attenuated. The setof active subscriber stations MS, MSn to be administered by a basestation BS is therefore different in uplink and downlink.

For the case in which the training sequences ma-n are allocatedcentrally on the network side, the training sequences can also betransmitted directly from the central allocation point, for example thedevice for allocating radio resources RNM, to the base station BSn,which sets up a communication link, and to possibly disturbing adjacentbase stations BS.

In the case of TDD systems, in which the transmission is performed inthe same frequency band in uplink and downlink, the spatial covariancematrices can be determined directly in conjunction, in particular, withtime slot information that has been communicated. By contrast, in FDDsystems (FDD: Frequency Division Duplex) a frequency transformation hasto be carried out before the estimated uplink covariance matrices can beused for the application in downlinks.

For the case of adjacent radio cells Zn having a width that is only verysmall by comparison with the cell of the disturbing base station BS, itis also possible for a subscriber station to be disturbed in a radiocell behind the directly adjacent radio cell Zn of the base station BS.In such scenarios, not only information relating to the subscriberstations MSn of the directly adjacent radio cells Zn is needed, but alsorelating to the subscriber stations of the more remote radio cells,which are therefore also treated like adjacent radio cells Zn.

The error covariance matrix R_(I) ^((I)) can advantageously also takeaccount of and include the disturbing interference that is known per sefrom DE 198 03 188.

Advantageous error covariance matrices follow from the a priori modelfor two- or three-dimensional isotropic noise in which it is assumedthat mutually uncorrelated homogeneous plane waves of equal intensityare irradiated onto the BS from all directions. The associated errorcovariance matrices can be specified in closed form and stored.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention.

1. A method for data transmission in a radio communication system havingat least two base stations and radio stations that are connected in eachcase to one of the base stations via wireless interfaces, at least afirst base station having an antenna arrangement with a plurality ofantenna elements and a signal processing device for transmitting andreceiving data as a function of direction, comprising: transmitting datafrom the first base station to a first radio station communicatingtherewith in a cell, concurrently with transmission of data from asecond base station adjacent to the first base station, to at least onesecond radio station communicating therewith in an adjacent cell whichis adjacent to the cell; determining, at the first base station, whetherdownlink transmission of the data from the first base station causes adisturbance for the at least one second radio station in the adjacentcell; and reducing downlink transmission power of the antennaarrangement of the first base station only in a downlink direction thatis directed towards the at least one second radio station in theadjacent cell when it is determined that downlink transmission of thedata from the first base station does cause a disturbance for the atleast one second radio station in the adjacent cell.
 2. The method asclaimed in claim 1, further comprising transmitting to the first basestation, as the signal information relating to the signal transmitted bythe at least one second radio station, at least one training signal ofthe at least one second radio station.
 3. The method as claimed in claim2, wherein the signal information includes downlink time slots duringwhich the at least one second radio station receives data from thesecond base station.
 4. The method as claimed in claim 2, wherein thesignal information includes an uplink time slot of the at least onesecond radio station.
 5. The method as claimed in claim 4, wherein thesignal information is transmitted via network devices in the radiocommunication system.
 6. The method as claimed in claim 1, wherein thesignal information is transmitted via network devices in the radiocommunication system.
 7. The method as claimed in claim 1, wherein saidtransmitting of data uses one of an FDD and a TDD mode in at least oneof time slots and a multi-slot method.
 8. The method as claimed in claim1, wherein the signal information is transmitted to the first basestation one of regularly and after setting up a connection of the secondbase station to the at least one second radio station.
 9. The method asclaimed in claim 1, wherein the signal information includes downlinktime slots during which the at least one second radio station receivesdata from the second base station.
 10. The method as claimed in claim 1,further comprising taking into account disturbing interference that doesnot originate from the radio communication system using the spatialerror covariance matrix.
 11. The method as claimed in claim 1, whereinthe radio communication system includes asynchronous switching points,and wherein said method further comprises transferring the signalinformation relating to the training signals and the uplink time slotsof the second base station to the first base station when the uplinktime slots are used by the first base station as downlink time slots.12. The method for data transmission in a radio communication system ofclaim 1, further comprising: compensaling for disturbance via errorcovariance matrices that follow from the a priori model for two orthree-dimensional noise in a direction of the disturbed radio station,which is adjacent to the disturbing first base station.
 13. A method fordata transmission in a radio communication system having at least twobase stations and radio stations that are connected in each case to oneof the base stations via wireless interfaces, at least a first basestation having an antenna arrangement with a plurality of antennaelements and a signal processing device for transmitting and receivingdata as a function of direction, comprising: transmitting data from thefirst base station to a first radio station communicating therewith in acell, concurrently with transmission of data from a second base stationadjacent to the first base station, to at least one second radio stationcommunicating therewith in an adjacent cell which is adjacent to thecell; determining that transmission of the data from the first basestation causes a disturbance for the at least one second radio stationin the adjacent cell; reducing transmission power of the antennaarrangement of the first base station directed towards the at least onesecond radio station in the adjacent cell which is disturbed, afterreception of signal information relating to a signal transmitted by theat least one second radio station and reception of a signal assignableto the at least one second radio station; transmitting to the first basestation, as the signal information relating to the signal transmitted bythe at least one second radio station, at least one training signal ofthe at least one second radio station, wherein the signal informationincludes an uplink time slot of the at least one second radio station,and the signal information is transmitted via network devices in theradio communication system; and setting a distribution of a spatialtransmit power at the first base station based on a spatial errorcovariance matrix R_(I) ^((I)) which yields a beam-shaping vector(w^((k))) as a solution to an optimization problem defined as follows${{r\left( w^{(k)} \right)} = {\frac{w^{{(k)}H}R_{S}^{(k)}w^{(k)}}{w^{{(k)}H}R_{I}^{(k)}w^{(k)}} = {\max!}}},$and weighting signals transmitted by the first base station using thebeam-shaping vector.
 14. The method as claimed in claim 13, furthercomprising solving the optimization problem by solving a generaleigenvalue problem with positive semi-definite Hermitian matrix R_(S)^((k)) and positive definite Hermitian matrix R_(I) ^((k)),R _(S) ^((k)) w ^((k)) =λR _(I) ^((k)) w ^((k)) to obtain thebeam-shaping vector w^((k)) as an eigenvector relating to a maximumeigenvalue.
 15. The method as claimed in claim 14, wherein saidtransmitting of data uses one of an FDD and a TDD mode in at least oneof time slots and a multi-slot method.
 16. The method as claimed inclaim 15, wherein the signal information is transmitted to the firstbase station one of regularly and after setting up a connection of thesecond base station to the at least one second radio station.
 17. Themethod as claimed in claim 16, wherein the signal information includesdownlink time slots during which the at least one second radio stationreceives data from the second base station.
 18. The method as claimed inclaim 17, further comprising taking into account disturbing interferencethat does not originate from the radio communication system using thespatial error covariance matrix.
 19. The method as claimed in claim 18,wherein the radio communication system includes asynchronous switchingpoints, and wherein said method further comprises transferring thesignal information relating to the training signals and the uplink timeslots of the second base station to the first base station when theuplink time slots are used by the first base station as downlink timeslots.
 20. A method for data transmission in a radio communicationsystem having at least two base stations and radio stations that areconnected in each case to one of the base stations via wirelessinterfaces, at least a first base station having an antenna arrangementwith a plurality of antenna elements and a signal processing device fortransmitting and receiving data as a function of direction, comprising:transmitting data from the first base station to a first radio stationcommunicating therewith in a cell, concurrently with transmission ofdata from a second base station adjacent to the first base station, toat least one second radio station communicating therewith in an adjacentcell which is adjacent to the cell; determining that transmission of thedata from the first base station causes a disturbance for the at leastone second radio station in the adjacent cell; reducing transmissionpower of the antenna arrangement of the first base station directedtowards the at least one second radio station in the adjacent cell whichis disturbed, after reception of signal information relating to a signaltransmitted by the at least one second radio station and reception of asignal assignable to the at least one second radio station; and settinga distribution of a spatial transmit power at the first base stationbased on a spatial error covariance matrix R_(I) ^((I)) which yields abeam-shaping vector (w^((k))) as a solution to an optimization problemdefined as follows${{r\left( w^{(k)} \right)} = {\frac{w^{{(k)}H}R_{s}^{(k)}w^{(k)}}{w^{{(k)}H}R_{I}^{(k)}w^{(k)}} = {\max!}}},$and weighting signals transmitted by the first base station using thebeam-shaping vector.
 21. The method as claimed in claim 20, furthercomprising solving the optimization problem by solving a generaleigenvalue problem with positive semi-definite Hermitian matrix R_(S)^((k)) and positive definite Hermitian matrix R_(I) ^((k)),R _(S) ^((k)) w ^((k)) =λR _(I) ^((k)) w ^((k)) to obtain thebeam-shaping vector w^((k)) as an eigenvector relating to a maximumeigenvalue.
 22. A radio communication system, comprising: at least firstand second base stations; at least first and second radio stationscommunicating with the first and second base stations, respectively, viawireless interfaces, the at least first radio station being in a celland the at least second radio station being in an adjacent cell which isadjacent to the cell; and at least one antenna arrangement, coupled tothe first base station, having a plurality of antenna elements and asignal processing device to transmit and receive data as a function ofdirection; including transmitting data from the first base station tothe first radio station in the cell concurrently with transmission ofdata from the second base station to the second radio station in theadjacent cell, wherein when the first base station determines thatdownlink transmission of data from the first base station disturbs thesecond radio station in the adjacent cell, the signal processing devicereduces downlink transmission power of the antenna arrangement of thefirst base station only in a downlink direction towards the second radiostation in the adjacent cell after reception of signal informationrelating to a signal transmitted by the second radio station andreception of a signal assignable to the second radio station.